1. Field of the Invention
This specification relates to a method for separation of HMX and RDX, and particularly, to a method for effectively separating HMX and RDX from HMX/RDX-included explosives, respectively.
2. Background of the Invention
Explosives having a high performance and being widely used in many fields include HMX (Cyclotetramethylenetetranitramine) and RDX (Cyclotrimethylenetrinitramine). Each of the HMX and RDX is presented in a state of impurities by a certain amount in a synthesis process. For instance, when HMX is synthesized by the Bachmann process, RDX is also synthesized by about 27%. This requires an additional separation.
In order to obtain HMX of a high purity through an additional separation, a mixture of HMX and RDX (HMX explosives mixed with 27% RDX) is put in a solution where 2.93 g of sodium tetraborate (Na2B4O7 or Na2B4O7.10H2O) was dissolved in 975.6 g of water. Then, the mixture is boiled with being agitated. Then, 5N sodium hydroxide is added to 42.4 cc of the solution with a speed of 3 mL/min (for 47.3 minutes). The solution is continuously boiled, and sodium hydroxide is put to increase pH to 9.7 from 8.7. As a result, pure HMX having RDX completely separated from the mixture is obtained. Then, the mixture is re-crystallized by using a solvent (nitromethane, acetone, acetonitrile, cyclohexanone, etc.), thereby forming pure HMX particles having a ‘β’-form.
In order to more easily separate HMX or RDX generated in the form of impurities during a synthesis process, a supercritical separation process has been proposed. A supercritical fluid is defined as ‘any substance at a temperature and pressure above its critical point’, and has a unique characteristic not exhibited in the conventional solvent. A physical property of a solvent is determined by an intermolecular interaction determined by a molecule type and a molecule distance. Since a liquid solvent is a non-compressed type, an intermolecular distance is scarcely changed. Accordingly, it is difficult to expect a great change of a property from the liquid solvent used as a single solvent. A density of the supercritical fluid may be consecutively changed from highly rarefied conditions close to an ideal gas to a high density close to a liquid density. Therefore, this may control not only an equilibrium property (solubility, entrainer effects) of a fluid, a transfer property (viscosity, diffusion coefficient, thermal conductivity), but also dissolution (solvation) and a molecule clustering state. A supercritical fluid process is performed to maximize energy usage efficiency during extraction, separation and drying processes, by selectively separating a product having a high purity and a high value at a high transfer speed based on excellent thermodynamic characteristics (spontaneous separation due to high solubility, selectivity, compressibility, and decompression), flowing characteristics (low viscosity and surface tension, and high diffusion coefficient), by re-using an extracted solvent, by removing a solvent remaining on the product, etc.
There has been proposed a method for separation of HMX and RDX by dissolving a mixture including HMX and RDX in heated water and a heated solvent of cyclopentanon, and then by performing selective re-crystallization. Alternatively, there has been proposed a method for separation of HMX by dissolving a mixture of RDX and HMX in a solvent of dimethyl sulfoxide having a temperature of 70˜90° C., by adding a sufficient amount of water to the mixture, and by performing re-crystallization. Still alternatively, there has bee proposed a method for forming β-HMX by dissolving acetic anhydride/HMX slurry in an acid remaining after performing nitrolysis with respect to hexamine, and by performing re-crystallization.
In the aforementioned methods for separation of HMX and RDX, selective re-crystallization was performed by using an organic solvent, an acetate solution, an aqueous solution or a mixture thereof. However, these methods may have the following problems. Firstly, an organic solvent harmful to a human body has to be used. Secondly, a liquid chromatograph absorption method causing a large amount of waste water has to be used. Thirdly, these methods are not suitable for massive productions.